def letters(s):
    return ''.join(a for a in s if a.isalpha())


def reverse(s):
    if s=="":
        return s
    else:
        return reverse(s[1:])+s[0]

str=input("请输入一个字符串：")
print("剔除非英文字母后：")
print(letters(str))
m=letters(str)
print("字符串反转输出：")
print(reverse(m))
